The invention relates to on-car brake lathes.
A brake system is one of the primary safety features in every road vehicle. The ability to quickly decelerate and bring a vehicle to a controlled stop is critical to the safety of the vehicle occupants and those in the immediate vicinity. For this reason, a vehicle braking system is designed and manufactured to exacting specifications and is subject to rigorous inspection.
Disc brake assemblies, which are typically mounted on the front wheels of most passenger vehicles, are primary components of a brake system. Generally, a disc brake assembly includes a caliper that cooperates with a brake hydraulic system, a pair of brake pads, a hub, and a rotor. The caliper supports and positions the pair of brake pads on opposing sides of the brake rotor. In a hubless brake rotor (i.e. when the rotor and hub are separate components), the rotor is secured to the vehicle hub with a series of bolts and a rotor hat. The rotor rotates with the hub about a vehicle spindle axis. When a vehicle driver depresses a brake pedal to activate the hydraulic system, the brake pads are forced together and toward the rotor to grip friction surfaces of the rotor.
Disc brake assemblies must be maintained to the manufacturer""s specifications throughout the life of the vehicle to assure optimum performance and maximum safety. However, several problems have plagued the automotive industry since the inception of disc brakes.
A significant problem in brake systems is usually referred to as xe2x80x9clateral runout.xe2x80x9d Generally, lateral runout is the side-to-side movement of the friction surfaces of the rotor as the rotor rotates with the vehicle hub about a spindle axis. Referring to FIG. 1, for example, a rotor having friction surfaces on its lateral sides is mounted on a vehicle hub for rotation about the horizontal spindle axis X. In an optimum rotor configuration, the rotor is mounted to rotate in a plane Y that is precisely perpendicular to the spindle axis X. Generally, good braking performance is dependant upon the rotor friction surfaces being perpendicular to the spindle""s axis of rotation X and being parallel to one another. In the optimum configuration, the opposing brake pads contact the friction surfaces of the rotor at perfect 90 degree angles and exert equal pressure on the rotor as it rotates. More typically, however, the disc brake assembly produces at least a degree of lateral runout that deviates from the ideal configuration. For example, a rotor often will rotate in a canted plane Yxe2x80x2 and about an axis Xxe2x80x2 that is a few thousandths of an inch out of axial alignment with the spindle (shown in exaggerated fashion in FIG. 1). In this rotor configuration, the brake pads, which are perpendicular to the spindle axis X, do not contact the friction surfaces of the rotor along a constant pressure plane.
The lateral runout of a rotor is the lateral distance that the rotor deviates from the ideal plane of rotation Y during a rotation cycle. A certain amount of lateral runout is inherently present in the hub and rotor assembly. This lateral runout often results from defects in individual components. For example, rotor friction surface runout results when the rotor friction surfaces are not perpendicular to the rotor""s own axis of rotation, rotor hat runout results when the hat connection includes deviations that produce an off center mount, and stacked runout results when the runouts of the components are added or xe2x80x9cstackedxe2x80x9d with each other. An excessive amount of lateral runout in a component or in the assembly (i.e., stacked runout) will generally result in brake noise, pedal pulsation, and a significant reduction in overall brake system efficiency. Moreover, brake pad wear is uneven and accelerated with the presence of lateral runout. Typically, manufacturers specify a maximum lateral runout for the friction surfaces, rotor hat, and hub that is acceptable for safe and reliable operation.
After extended use, a brake rotor must be resurfaced to bring the brake assembly within manufacturers"" specifications. This resurfacing is typically accomplished through a grinding or cutting operation. Several prior art brake lathes have been used to resurface brake rotors. These prior art lathes can be categorized into three general classes: (1) bench-mounted lathes; (2) on-car caliper-mounted lathes; and (3) on-car hub-mounted lathes.
In general, bench-mounted lathes are inefficient and do not have rotor matching capabilities. To resurface a rotor on a bench-mounted lathe, the operator is first required to completely remove the rotor from the hub assembly. The operator then mounts the rotor on the bench lathe using a series of cones or adaptors. After the cutting operation, the operator remounts the rotor on the vehicle spindle. Even if the rotor is mounted on the lathe in a perfectly centered and runout-free manner, the bench lathe resurfacing operation does not account for runout between the rotor and hub. In addition, bench lathes are susceptible to bent shafts which introduce runout into a machined rotor. This runout is then carried back to the brake assembly where it may combine with hub runout to produced a stacked runout effect.
Similarly, caliper-mounted lathes have had limited success in compensating for lateral runout, and require time consuming manual operations. During a rotor resurfacing procedure, the brake caliper must be removed to expose the rotor and hub. Once this is done, the caliper mounting bracket is used to mount the on-car caliper-mounted lathe. Caliper-mounted lathes lack a xe2x80x9crigid loopxe2x80x9d connection between the driving motor and cutting tools, and are unable to assure a perpendicular relationship between the cutting tools and the rotor. Nor does a typical caliper-mounted lathe have a reliable means for measuring and correcting lateral runout. Typically, such lathes use a dial indicator to determine the total amount of lateral runout in the disc assembly. This measurement technique is problematic in terms of time, accuracy, and ease of use.
On-car hub-mounted lathes, generally are the most accurate and efficient means for resurfacing the rotor. Such a lathe is disclosed in U.S. Pat. No. 4,226,146, which is incorporated by reference.
Referring now to FIG. 2, an on-car disc brake lathe 10 may be mounted to the hub of a vehicle 14. The lathe 10 includes a body 16, a driving motor 18, an adaptor 20, and a cutting assembly 22 including cutting tools 23. The lathe may be used with a stand or an anti-rotation post (not shown), either of which can counter the rotation of the lathe during a resurfacing operation. After the brake caliper is removed, the adaptor 20 is secured to the hub of the vehicle 14 using the wheel lug nuts. The lathe body 16 is then mounted to the adaptor 20, the orientation of which may be adjusted using adjustment screws 24.
The operator then determines the total amount of lateral runout and makes an appropriate adjustment. Specifically, the operator mounts a dial indicator 26 to the cutting head 22 using a knob 28. The dial indicator 26 is positioned to contact the vehicle 14 at one of its distal ends as shown in FIG. 2. Once the dial indicator 26 is properly positioned, the operator takes the following steps to measure and compensate for lateral runout:
(1) The operator mates the lathe to the rotor using the adaptor.
(2) The operator activates the lathe motor 18, which rotates the adaptor 20, the brake assembly hub, and the rotor. The total lateral runout of the assembly is reflected by corresponding lateral movement in the lathe body.
(3) The lateral movement of the lathe body is then quantified using the dial indicator 26. Specifically, the operator observes the dial indicator to determine the high and low deflection points and the corresponding location of these points on the lathe.
(4) Upon identifying the highest deflection of the dial indicator, the operator stops the rotation at the point of the identified highest deflection.
(5) The operator then adjusts the lathe to compensate for runout of the assembly. This is accomplished by careful turning of the adjustment screws 24. There are four adjustment screws. The screw or screws to be turned depend on the location of the high deflection point. Turning the screws adjusts the orientation of the lathe body with respect to the adaptor 20 (and therefore with respect to the rotor and hub) to mechanically compensate for the runout of the assembly. The operator adjusts the screws until the highest deflection point is reduced by half as determined by reference to the dial indicator 26.
(6) The operator activates the lathe motor 18 and observes the dial indicator 26 to again identify the highest deflection of the dial. If the maximum lateral movement of the lathe body, as measured by the needle deflection, is acceptable (i.e. typically less than {fraction (3/1000)} of an inch) then mechanical compensation is complete and the lathe resurfacing operation can commence. Otherwise, further measurement and adjustment is made by repeating steps (1) to (6). The resurfacing operation is then performed by adjusting the tool holder 22 and cutting tools 23 to set the proper cutting depth.
Although the hub mounted on-car brake lathe was a considerable advance over prior brake lathes, its structure and the corresponding procedure for compensating for lateral runout of the disc brake assembly has practical limitations. First, the procedure requires a significant amount of time to determine and adjust for lateral runout of the brake assembly. Although the specific amount of time necessary will vary based upon operator experience, the time for even the most experienced operator is significant and can substantially increase the cost associated with rotor resurfacing. Second, the procedure requires extensive education and operator training to assure that proper mechanical compensation for lateral runout is accomplished. Moreover, the accuracy and success of measurement and adjustment of lateral runout will vary from operator to operator.
In one general aspect, an on-car disc brake lathe system for resurfacing a brake disc of a vehicle brake assembly includes a lathe body with a driving motor, a cutting head operably attached to the lathe body, and a drive shaft. The system further includes an alignment system including an electronic controller, an input adaptor configured to rotate with the drive shaft, an output adaptor configured to rotate with the drive shaft, and at least one adjustment disc positioned between the input adaptor and the output adaptor. Axial alignment of the input adaptor relative to the output adaptor may be varied based on a rotational orientation of the adjustment disc. An adjustment mechanism changes the rotational orientation of the adjustment disc in response to commands from the electronic controller.
Embodiments may include one or more of the following features. For example, the adjustment mechanism may include a stop disc operable in a first state to follow the rotation of the drive shaft and operable in a second state to rotate relative to the rotation of the drive shaft to change the rotational orientation of the adjustment disc. The adjustment mechanism may include a stop mechanism associated with the stop disc and operable to move between a first position in which the stop disc operates in the first state and a second position in which the stop disc is caused to operate in the second state. The stop disc may include a pair of stop discs, with the first stop disc operating in the first state when the stop mechanism is in the first position, in the second state when the stop mechanism is in the second position at a first time, and in the first state when the stop mechanism is in the second position at a second time different from the first time. The second stop disc operates in the first state when the stop mechanism is in the first position and when the stop mechanism is in the second position at the first time, and operates in the second state when the stop mechanism is in the second position at the second time.
The system may include a second adjustment disc positioned between the input adaptor and the output adaptor. The axial alignment of the input adaptor relative to the output adaptor may be varied based on the rotational orientation of the adjustment discs relative to each other. A stop disc or a pair of stop discs may be associated with each adjustment disc. A single stop mechanism may be associated with all of the stop discs. Gear trains may be associated with the stop discs, and may be configured to follow the movement of the respective stop discs, and to cause movement of the adjustment discs.
The adjustment discs may be slant discs that each include a slanted surface. The adjustment discs may be arranged so that the slanted surfaces are opposed to each other in an abutting relationship.
The stop discs may be starwheels having protruding teeth. The stop mechanism may be operable to move between a first position in which the stop disc operates in the first state and a second position in which the stop disc is caused to operate in the second state. For example, the stop mechanism may include an electromagnetic element and a toothed catch member operable to engage at least one tooth of the starwheel. The controller may be configured to time actuation of the electromagnetic element such that the toothed catch moves into its first stop position to contact a specified tooth of the starwheel.
The system also may include a component for measuring lateral runout of a brake disc and providing the measurement to the electronic controller. The electronic controller may issue commands to the adjustment mechanism based on the measurement.
The systems and techniques provide automatic compensation for the lateral runout of a lathe apparatus with respect to a vehicle hub. To this end, the brake lathe system includes a runout measurement and control system that determines the runout of a disc brake assembly and directs a corrective signal to an automated control system to compensate for lateral runout. The techniques may also be used in other practical applications to align two concentrically attached rotating shafts.
To provide automatic compensation for lateral runout, a brake lathe includes an automatic alignment coupling that operates in response to a corrective signal to adjust the alignment of the lathe with respect to the vehicle to mechanically compensate for lateral runout. The automatic alignment mechanism may include one or more stop discs that rotate with the drive shaft of the lathe and that can be selectively stopped from rotating with the shaft by a stop mechanism. In response to such stopping, one or more adjustment discs are caused to rotate to adjust the relative position of the axis of the lathe with respect to the axis of the disc brake assembly. In this manner, the system compensates for and corrects lateral runout that exists between two concentrically attached rotating shafts. Other techniques may also be used to compensate for the lateral runout.